Presently, as medicaments, use of protein preparations such as molecular targeting drugs, vaccines, and hormonal agents typified by insulin rapidly increases, and a device capable of easy administration of these medicaments is required. These medicaments are a high-molecular protein or peptide and are not absorbed into a body through oral administration. Therefore, administration by a syringe needle into a hypodermis or blood vessel is necessary.
Administration by a syringe needle, such as hypodermic, intravenous, and intramuscular administrations, is a general administration method presently. However, a drug solution is infused through puncture by the syringe needle and thus this method involves pain when the needle penetrates the skin. Therefore, in some cases, fear of the pain when puncture by a syringe needle is performed and discomfort in infusion of a drug solution is caused in a patient to which the drug solution is administered by using a syringe and the patient refuses the drug treatment or becomes negative about it. This leads to delay in the treatment. In particular, diabetes patients for which insulin injection is necessary and patients with growth deficiency for which growth hormone injection is necessary are frequently children, and the pain and discomfort in injection are also a cause of later “injection phobia” (Needle phobia).
Therefore, for patients including such child patients, a device that can be easily operated in injection and does not involve pain and allows automatic injection without direct contact with a syringe needle and a syringe is desired.
To meet this desire, as an automatic injection device that enables a patient to personally administer a drug solution easily, devices that automatically perform puncture and infusion by pressing a syringe and a pusher (plunger) of the syringe by a spring force have been proposed.
For example, the following device is described in Patent Document 1. The device includes a drive assembly and a syringe assembly mounted to the drive assembly. The drive assembly includes a drive rod, a driver releasably coupled to the drive rod, and a constant force spring that urges the drive rod toward the syringe assembly. In this device, the spring urges the coupled drive rod and driver along the axis line of the device to puncture the skin by a needle of the syringe assembly. Then, the drive rod is decoupled from the driver and the spring continues to urge the drive rod in the axis line direction. Thereby, the drive rod engages with a piston in the syringe assembly and pushes out a medicament therein to automatically perform an injection.
Furthermore, the following device is described in Patent Document 2. The device includes a housing that is so configured as to internally contain a medicament container. The housing includes a contact part to be applied to an injection site, a needle cover that surrounds a needle disposed to the medicament container and extends by at least the length of the needle, spring means capable of, when being actuated, pushing the needle to make it pass through an end part of the needle cover and operating the medicament container to supply a dose of medicament. The housing further includes first locking means capable of locking the spring means in a pressurized state and first actuating means capable of releasing the spring means for an injection when being manually operated. In this device, by pressing a button, a syringe to which the spring is mounted is actuated and the medicament is automatically injected.
Moreover, the following device is described in Patent Document 3. The device includes an elongated housing, a container containing a medicament to be infused through a needle, pressurizing means that acts on the container and is capable of, when being actuated, moving the container and the needle for puncture and subsequently expelling the medicament through the needle, and actuating means disposed to actuate the pressurizing means. In this device, the actuating means includes a needle shield disposed slidably relative to the housing and a collapsible holding member connected to an inner end part of the needle shield. Due to this, in the movement of the needle shield, the collapsible holding member collapses when a certain force is applied by the needle shield. Thereby, the further movement of the needle shield actuates the actuating means. Then, the actuating means releases the pressurizing means to initiate infusion of the medicament.